1. Field of the Invention
The present invention relates generally to an optical disk recording and reproducing apparatus for recording and reproducing information on an optical disk. More specifically, the invention relates to an optical disk recording and reproducing apparatus which is capable of detecting a defective disk.
2. Description of the Background Art
As is well known, an optical disk recording and reproducing apparatus scans a laser beam on an optical disk for recording and reproducing information thereon. The optical disk is formed with concentric or helical tracks for recording information thereon. The recording and reproducing apparatus includes a tracking servo mechanism for accurately irradiating the laser beam onto the track and a focus servo system for adjusting the focus of the laser beam.
Such servo mechanisms have limited servo characteristics. Because of the limit in the servo mechanism, a tracking servo mechanism cannot work effectively when circularity of the optical disk is poor to cause error in recording and reproducing information. On the other hand, when the optical disk having poor flatness is used, the focus servo mechanism will not work effectively to frequently cause data error.
Conventionally, in order to distinguish good disks and bad disks among manufactured disks, a standard is set by a radial run out which is a deviation of the circularity of the recording track from an accurate circle and an axial run out which is deviation of the disk surface from accurate flatness.
However, in practical operation, if trouble happens on the servo system, it was not possible to judge whether error is caused on the hardware or the disk. Conventionally, a standard disk is set in place of the used disk for checking the hardware. By checking the hardware, trouble-shooting can occur. However, this process requires a relatively long period to be wasted. Furthermore, in case that the disk is used as a back-up for storing back-up data of a computer and so forth, reliability is degraded. In addition, the aforementioned way of trouble-shooting may cause delay of data processing.